When the accelerator pedal of a vehicle is pressed while the clutch is disengaged, the accelerator (throttle) is opened to cause the engine to run at “idle” and the engine RPM (the number of revolutions of the engine) is stabilized at the engine RPM corresponding to the accelerator opening degree (accelerator position). At that point in time, the driving force generated by the engine and the internal resistance (friction) of the engine are in equilibrium and the engine output torque is 0. That is, the engine does no work for the outside the engine and fuel is wasted.
The engine does no work for the outside not only during idling caused by disengagement of the clutch as described above but also while the vehicle is in motion. In this situation, the engine only revolves at an engine RPM corresponding to the accelerator opening degree as in idling and does not contribute to acceleration or deceleration of the vehicle. Accordingly, the fuel is consumed only in causing the engine to revolve uselessly, which is highly wasteful.
The present applicant has proposed a coasting control device that performs coasting control that disengages the clutch and places the engine in idle state to save fuel consumption while the engine is running but is doing no work for the outside the engine (Patent Literature 2).
Coasting control is a technique, employed in a vehicle equipped with a mechanism capable of automatically disengaging the clutch, to improve fuel economy by automatically disengaging the clutch to reduce the engine RPM to an idle RPM or an RPM equivalent to that while the engine is revolving but doing no work for the outside the engine.
Since coasting control can be used in any vehicle that is capable of automatically turning off the engine output (automatically disengaging the clutch) as described above, the same effect can be achieved not only in a manual clutch system (manual T/M) but also in an automatic clutch system (conventional torque converter AT or AMT).